Return current object in SetContainer

[Component] [DependencyInjection] $this is missing in the setContainer function.  It broke my code in the following example:

``` php
 $widgetType->setType($type)
            ->setCssDocument($this->getCSSDocument($location))
            ->setLocation($location)
            ->setEntity($widget)
            ->setWidgetManager($this)
            ->setContainer($this->getContainer())
            ->setSettings($this->getSettings($location, $id))
            ->initialize();
```

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | none
| License       | MIT
| Doc PR        | none